Field of the Invention
The present invention relates to a motor control apparatus comprising a position detector for detecting the position of a rotor of a motor.
Description of the Related Art
In order to detect the position of a rotor of a motor, a position detector such as a rotary encoder or a linear scale is provided in a motor control apparatus for controlling rotational drive of the motor. A position detection value detected and fed back by the position detector is utilized for generating a speed command or a torque command for a motor.
A position detector realizes a high resolving power by further electrically interpolating (dividing) a physical scale. Interpolation, however, has an error, and the error is generated every time a rotor of a motor rotates one time. A position detection error caused by an interpolation error thus cyclically appears in an output of a position detector. By the position detection error, a speed command or a torque command which is generated by a motor control apparatus cyclically oscillates, and as the result, noise is generated from a motor which is driven and controlled by the motor control apparatus, which is problematic. A position detection error varies depending on the process, structure, and properties of a position detector, and is specific to the position detector.
For example, Japanese Laid-open Patent Publication No. 11-259110 describes a technique in which, for the variation of a position detection error specific to a position detector, the frequency thereof is calculated and a notch filter including the frequency as the center frequency is applied thereto to correct the position detection error, thereby reducing an oscillation which is generated caused by the position detection error.
A position detector provided in a motor control apparatus has a cyclic position detection error caused by an interpolation error. Among the above commands, a torque command which is generated by a motor control apparatus using a position detection value including a position detection error cyclically oscillates, and therefore a noise is generated from a motor when rotational drive of the motor is controlled by using such a torque command.
The invention described in Japanese Laid-open Patent Publication No. 11-259110 has a function of correcting a position detection error in a position detector. However, an existing position detector not having such a correction function therein needs to be provided with the correction function therein in such a manner that the correction function is physically added thereto, and therefore, in some cases, it is difficult to add the correction function thereto or the cost increases depending on the structure of the position detector, which are problematic.